Zinc chelation to promote axon regeneration after spinal cord injury

The objective of this proposal is to develop a novel approach to SCI treatment using zinc chelation. The failure of damaged axons to regrow is a major contributing factor to sustained functional deficits following SCI. Regrowth of axons, whether it is long distance regeneration that re-establishes original connections or shorter sprouting that re-wires local plastic circuits, is likely to underlie spontaneous and treatment-induced functional recovery. Recent data from Dr. Benowitz’s laboratory (mentor) showed that the ion zinc (Zn2+) is increased in injured neurons after mouse optic nerve crush, and that blocking the post-crush Zn2+ accumulation using Zn2+ chelation methods strongly promotes axon regeneration. Given the similarities between optic nerve and spinal cord, I propose to test the hypothesis that Zn2+ chelation will promote axon regrowth after SCI. I will test this hypothesis through three focused specific aims. First, I will quantify the Zn2+ in the motor and sensory neurons and examine the time-course of changes in Zn2+ following SCI. Further, I will optimize post-SCI Zn2+ chelation in motor and sensory neurons, examining both local delivery and systemic application using clinically approved chelating agents. Finally, I will determine whether Zn2+ chelation promotes motor and sensory axon regrowth after SCI in mice. Specifically, I plan to conduct mid-thoracic hemisection injuries, tract tracing, and Zn2+ chelation treatment in genetically normal mice. I will assess Zn2+ accumulation in brain, spinal cord, and dorsal root ganglia by autometallography. I plan to assess axon sprouting and regeneration of the traced corticospinal tract (motor) and the traced gracile fasciculus (sensory), using measures of the furthest regenerating axons, collateral axon sprouting, and axon density. Rubrospinal tract regeneration and new corticospinal-interneuron connections will also be examined. I have found that baseline (uninjured adult) levels of Zn2+ in the cell bodies of brain neurons that project to the spinal cord are already elevated in comparison to the projection neurons of the retina, suggesting that axons associated with these neurons may experience constitutive axon growth suppression by Zn2+, and that Zn2+ chelation may release this suppression and induce spinal cord axon regeneration regardless of whether the predicted SCI-induced increase in Zn2+ accumulation occurs in these neurons. I will perform this project under the mentorship of Dr. Benowitz, who discovered the benefit of Zn2+ chelation for optic nerve axon regeneration, and has expertise in the required assessments of Zn2+ chelation and quantification. Dr. Benowitz has experience with SCI research, as do I. If data from the proposed project support my hypotheses, I will be particularly encouraged because systemic Zn2+ chelation has been safely used for other clinical indications, increasing the translational potential of this approach for clinical SCI. (CHN: SCIRTS chn:wdg)